1. Field of the Invention
This invention relates to a photographic support, and particularly relates to a water-proof photographic support. More particularly, this invention relates to a water-proof photographic support substantially free from being soiled by a developing solution at the edge portion produced by the cutting procedure.
2. Description of the Prior Art
There has been previously employed, as the photographic support, a baryta paper consisting of a paper coated with a baryta layer comprising mainly barium sulfate on one surface. Recently, however, a water-proof photographic support comprising a paper sheet coated with a hydrophobic polyolefin on both surfaces thereof has been developed and employed to cope with the requirement of a rapid development process with an automation system. At the present time, most of the baryta papers have been replaced with the water-proof photographic support.
Nevertheless, even though the water-proof polyolefin layers are provided to the both surfaces, the water-proof photographic support is apt to be soiled by a developing solution at the edge portion produced by the cutting procedure, because the hydrophilic wood pulp fibers constituting the paper sheet are liable to draw the developing solution into the paper sheet from the exposed edge portion. The so-produced edge soiling can be satisfactorily reduced by washing sufficiently the developed photographic paper with water for a long time. However, the washing procedure for a long time is naturally adverse to the requirement for reduction of the development time. For this reason, a measure for preventing permeation of a developing solution from the edge portion has been earnestly studied.
Until now, there is known and generally employed a measure for preventing permeation of a developing solution which involves incorporation of a sizing agent into the paper sheet. However, there necessarily arise various limitations to the sizing agent employable for the purpose, in view of the employment in the specific art of photographic paper. For instance, the sizing agent to be employed should be effective against permeation of either an alkaline or an alcohol such as most generally employed benzyl alcohol, both of which are contained in a developing solution. Moreover, the sizing agent should not decrease whiteness of the photographic paper and should not give any adverse effect to an image produced on the photographic paper such as production of fog. Accordingly, sizing agents generally employable for sizing a paper such as a rosin size and a petroleum resin size are not employable for sizing a paper sheet of the photographic support.
In view of the above-described requirements, there have been proposed a number of specific sizing agents for the use in the photographic support, such as a fatty acid soap sizing agent disclosed in Japanese Patent Publication No. 47(1972)-26,961 and an alkylketene dimer disclosed in Japanese Patent Provisional Publication No. 51(1976)-132,822. These sizing agents, however, are not considered to be satisfactory, because these sizing agents have certain drawbacks. More in detail, the fatty acid soap sizing agent is effective for prevention of permeation of the alcohol, while it is less effective against permeation of the alkaline solution. Moreover, the fatty acid soap is liable to be influenced by the quality of water employed in paper making. For instance, the fatty acid soap precipitates in a hard water to impart poor sizing effect to the paper sheet and/or to bring about disadvantageous features in the paper making process. On the other hand, the alkylketene dimer is effective for preventing permeation of an alkaline solution contained in a developing solution, while it is extremely poor in preventing permeation of the alcohol. Moreover, the satisfactory prevention of permeation of the alkaline solution by the alkylketene dimer is accomplished only in the case where a relatively large amount of a preserving agent, that is, a polyamide-polyamineepichlorohydrin resin is employed together with the alkylketene dimer. Thus, there has not been known a satisfactory sizing agent for the employment in a photographic support.